1. Field of the Invention
The invention relates to Global Navigation Satellite Systems (GNSS), and more particularly to GNSS combined with dead reckoning system and Geographic Information System (GIS).
2. Description of the Related Art
GNSS is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. GNSS is also known as Global Positioning System (GPS) in the United States. A GNSS receiver determines its location comprising longitudes, latitudes, and altitudes according to radio signals transmitted from satellites. A GNSS receiver also calculates the precise time. Thus, a device comprising a GNSS receiver can easily obtain precise positioning data. For example, a driver can easily lead his car to destination according to navigation instruction of a GNSS device.
A GNSS device also has disadvantages. A few factors determines the quality of satellites communications. The number of visible satellites in the sky determines the receiving quality of GNSS signals. Weather conditions and signal receiving environments also greatly affect the quality of satellite communication. Because a GNSS receiver determines its location according to radio signals sent by satellites, the GNSS receiver cannot generate positioning data when satellite communication fails. For example, when a car enters a tunnel, the receiving environment of the tunnel blocks the GNSS radio signals, and a GNSS device in the car cannot generate positioning data according to the GNSS signals.
To determine a location when a GNSS device fails, a dead reckoning device is introduced in place of the GNSS device to temporarily estimate the location. A dead reckoning device measures measurement thereof to estimate a location thereof. The dead reckoning device may be an accelerometer measuring acceleration, an odometer measuring moving distance, or a gyro measuring angular rate (compass measuring absolute angles). The location estimation of a dead reckoning device, however, has greater errors and is usable only for a short period.
To solve the problem, the invention provides a positioning system which comprises a GNSS module, a dead reckoning module, and a GIS module. The GIS module improves the precision of positioning data generated by the GNSS module and the dead reckoning module. Thus, the positioning system provides a location information with smaller error and can be used longer when the GNSS system fails.